Improved low temperature absorption refrigeration



March l1, 1958 F, E, GILMORE 2,826,049

- yIWDRCI'D LOW TEMPERATURE ABSORPTION REFRIGERATION Filed 06T.. 13, 1955 2 Sheets-Sheet l March 11, 1958 F. E. GILMORE 2,826,049

IMPROVED LOW TEMPERATURE ABSORPTION REFRIGERATION Filed Oc'b. 1S, 1955 2 Sheets-Shea?l 2 COOLANT VAPOROUS NH3 &

INVENTOR. F.E. GI LMORE W 'VM COOLANT Arron/vin momia. haust steam, Isupplement'the regenerativefractional dis- 'tillation step with a separate flashing operation-in which ,A a vapor is ila'shed from the regular distillation column f 2,826,049 Ice Patented Mar. 11, 1958 nirnovnn Low TEMPERATURE AnsoRP'rIoN REFRIGERATIoN Forrest E. Gilmore, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application October 13, 1955, Serial No. $40,189

14 Claims. (Cl. 62-1'79) This invention relates to an improved refrigeration system using yammonia as the refrigerant. In one aspect it relates to a low temperature ammonia absorption refrigeration system. In another aspect, it relates to such a system in which the utility requirements are held to plant cooling water as the only extraneous cooling and to the use of waste heat as the only source of heat.

An object of my invention is to provide an efncient ammonia absorption refrigeration system.

Another object of my invention is to provide an absorption refrigeration system in which the utility requirements are limited to plant cooling water and ordinary exhaust or waste heat.

Still another object of my invention is to provide an ellicient absorbing heat exchanger for use in such an absorption refrigeration system.

Yet another object of my invention is to provide apparatus and a method for cooling of the aqua ammonia during the absorption steps in place of after t-he absorption steps.

Still another object of my invention is to provide such a refrigeration system in which ammonia compression costs are low.

Still other objects and advantages will be realized upon reading the following description which, taken with the attached drawing, forms apart of 'this specification.

My invention involves the use of a W pressure, low temperature regenerative distillation step for which ordinary plant exhaust steam, sometimes called waste heat, provides the heat. By Waste lheat 'or exhaust steam, I mean such steam yas that usually exhausted by steam lpowered equipment such'as pumps and the like. Such steam frequently is exhausted from the pumps at about pounds per'squarein'chgauge pressure and itis such steam which l 'se for heating in my process. Ordinary plant cooling water provides all of the extraneous cooling for condensing of "the recovered or regenerated amln order'to utili'zefordinary waste heat or exaqua ammoniaibottomsthereby"eecting a further separation of ammonia from the aqua ammonia. Low temperature heat exchange used in my system is obtained temperatures, absorbing'th'eilashed ammonia lin aqueous ammonia of progressively Aincreased concentrations of ammonia in progressively yhigherv pressure absorption steps, passing the finally produced aqueous ammonia into a fractionation column and 4'therein fractionating ysaid aqueous ammonia under superatnosplieric pressure 'to produce an overhead vaporous ammonia product and a bottoms product of aqueous ammonia of reduced `ammonia content, condensing the overhead vaporous ammonia to produce liquid ammonia, reducing the pressure on the aqueous ammonia bottoms product in a bottoms ilas'hing operation, removing ash vapors of aqueous ammonia from this bottoms flashing operation and passing same into the absorption step of highest pressure of the successive absorption steps, passing the flash bottoms of said bottoms dashing operation into the absorption step o'f lowest pressure of the-successive absorption steps, cooling the aqueous ammonia and vaporous ammonia of the highest pressure absorption step by indirect heat exchange with plant cooling water and cooling the aqueous ammonia and vaporous ammonia of the lowestpressure absorption step by indirect heat exchange with the condensed liquid ammonia.

y In the drawing, Figure .l represents, in diagrammatic form, a now diagram illustrative of the operation of my process.

Figure 2 is an elevational view, partially in section, of a portion of the apparatus of Figure 1.

Figure 3 is a sectional `view taken -on the line 3--3 of Figure 2.

Referring now to the drawing and specifically tofiigure l, reference numeral 11 identities a more or less conventional fractional distillation column. This column is provided with vapor-liquid contactingtapparatus 4such as bubble cap trays or any other suitable conventional vapor-liquid contacting apparatus. Reference numeral 12 identities an overhead conduit .which leads from the upper portion ofthe column .to a `condenser 16 and thence to a tank 17. A pump 18 is provided for transfer of a portion of liquid from tank 17 by way ofapipe 19 into the top of column 11. VThe rate of flow of liquid through pipe V19 is controlled by a rate of ow controller assembly 20.

A bottoms product removal ,pipe 13 is provided for column 11, and this 'pipe is connected to a pipe 14 for passage of a portion of the bottoms product 'through a heat exchanger 15 and Athence into the reboiler section of column 11. A pipe 23 is also connected with pipe 13 for transfer of the, remainder of the bottoms product to a flash vessel 26. Incase heat is required to be added 'to the liquid flowing through `pipe 23, aheat exchanger 24 is provided. In case ,it is not desiredto add heat to the material iiowing through pipe 23, ,a bypass pipe 63 is provided for lay-passing the exchanger Z4.

A pipe 27 c'onnects'the top of a ash tank 26 with a pipe 37 which in turn connects an ammonia ilash vessel 38 with an absorbing heat exchanger 61. A pipe v56 connects this heat exchanger with an accumulator or separator'vessel'54. A conduit'22 leads from the separator vessel `54 byk way vof -a pump 55 through aheat exchanger 60 and thence Ato the fractionaldistillation vessel "111. `A conduit'28 provided with a rate :of 'ilow controller 20A, leads fromthe bottom of `theilash-separator 26 through heat exchanger into an ammonia vapor inlet pipe 29 'on Vthe inlet side of a Lsecond absorbing heat-exrchanger`30. AA pipe"71 leads fromthe other e'nd `'of the heat 'exchanger-absorber 30 to a separator tank 72 from-which aconduit'76 leads byway of a pump 75 'and line 26 to a 'conduit 78 `which 1is intended to transfer ammonia vapors froma vaporizer tank 77 to a separator tank 31. A conduit 5'35 leads from vthe bottom of-the lseparator tank 31 by :way of `a pump 36 -tothe aforementioned pipe 37. t Conduit-41 leads 'cooled liquid ammonia'fromevaporator tank 38 to lonefend vof 'the heat: exchanger-'absorber All() `and a conduit Altlleads from to the surge tank 77 is an evaporator vessel 46, a pipe 44 'i serving to transfer liquid from Ysurge tank 77 to Ythe evaporator 46 and a pipe 47 serving to lead vaporous am- LAmonia to the surge tank 77. A surge tank 51 is an accumulator for liquid ammonia from which the liquid passes y by Way of a pipe 50 to an evaporator 48 and vapors return therefrom by way of a pipe 49 to the surge tank 51.

' A liquid level float controller assembly 52 regulates the ow `of liquid ammonia through a pipe 4S from pipe 44 yinto surge tank 51. Liquid level float controllers 34, S3

and 74 regulate the level of liquids in separator tanks 31, 54 and 72 respectively. Pipes 32, 29A and 73 transfer vapors, .mostly inerts, from separators 31, 54 and 72, respectively, to subsequent operational points of the system. Y

Ammonia for starting up thesystem and makeup ammonia, as required, are introduced into the system from a source, not shown, via line 91A.

A pipe 21 leads from conduit 19 to transfer a portion of liquid ammonia from tank 17 to the upper portion of separator vessel 38. A liquid level oat controller assembly 39 operates to regulate the ow of liquid through pipe 21 into vessel 38 in response to the level of the liquid in this vessel. A liquid level float controller assembly 25 controls the Withdrawal of bottoms product from the fractionator 11 to maintain a constant level therein. Back pressure regulators 33and 80 regulate the pressure in separator vessels 31 and 54 respectively. Pipes 57 and 58 lead plant cooling water to and from, respectively, the absorbing heat exchanger 61. Reference numeral 59 identifies an air-iin atmospheric cooler disposed in pipe 27.

In the operation of my absorption refrigeration system, I will describe same beginning with the operation of the fractionator 11. Rich aqua ammonia is introduced as feed into this fractionator through pipe 22 and this fractionator operates in such a manner as to produce substantially anhydrous ammonia as an overhead product and a lean aqua `ammonia as a bottom product, and using only Waste steam at about 15 pounds per square inch gauge pressure for reboiling purposes. Steam at this pressure imparts a temperature of about 240 F. to the kettle contents of the column. The column is maintained at about 155 pounds absolute pressure and under these conditions the bottoms aqua ammonia product contains about 25 weight percent ammonia. The ammonia overhead vapors pass from the column through pipe 12, condenser 16 and condensate ammonia passes to the accumulator tank 17. This ammonia stream contains about 991/2 percent NH3. Such a portion of this ammonia as is required for refluxing the column in order to produce substantially anhydrous ammonia, about 0.25 reux ratio in this specific example, is passed by pump 18 through pipe 19 to the upper portion of the column. Plant cooling water at about 90 F. is used for the indirect heat ex* change in condenser 16. The liquid ammonia in tank 17 which is not required for refluxing is the refrigerant ammonia which is passed to the main portion of the refrigeration portion of my system.

In order to produce low temperature refrigeration for low temperature process Work, the liquid ammonia not required for column refluxing, as just mentioned, is passed through pipe 21 into separator vessel 3S. On passing through the valve in line 21, which is an element of the liquid level oat controller assembly 39, the pressure of the liquid ammonia is reduced from about 153 p. s. i. a. to about 49 p. s. i. a. On experiencing this reduction in pressure the temperature of the ammonia is reduced from about 95 F. to about 20 F. The ammonia which vaporizes from this pressure reduGiOIl Passes from separator 38 through pipe 37 into the absorbing heat exchanger 61. The absorbent for absorbing these ammonia vapors enters pipe 37 through pipe 35 from a source to be described subsequently. Aqua ammonia bottoms from fractionator 11 not required in the reboiling operation are passed from pipe 13 to pipe 23 and are heated in heater 24 or are passed through by-pass line 63 around the heater into the flash tank 26. This liquid on passing through the valve which is operating in conjunction with the liquid level controller 25 permits a reduction of pressure of the aqua ammonia bottoms from about p. s. i. a. to about 50 p. s. i. a., this latter pressure being controlled substantially by the rate of flow controller 20A which is disposed in pipe 28. The vaporous material which flash vaporizer in tank 26 contains about 5l Weight percent ammonia (the remainder being water vapor) and this vaporous ammonia and water vapor passes on through pipe 27 provided with the air-fin cooler 59 and thence is added to the vaporous ammonia in pipe 37. The aforementioned aqua ammonia (pipe 35) is added to the contents of pipe 37 at substantially its point of attachment to the absorbing heat exchanger 61. The aqua ammonia from pipe 35 absorbs a large portion of the vaporous ammonia in pipe 37 prior to entry into the absorber 61. The aqua ammonia and any unabsorbcd vaporous ammonia from pipe 37 pass into the absorbing exchanger 61 in which substantially all the vaporous arnmonia becomes absorbed. Because vaporous ammonia is very rapidly soluble in Water, this absorption takes place quite rapidly and in fact a large proportion of the vaporous ammonia is actually absorbed by the aqua ammonia by the time the aqua ammonia actually enters heat exchanger 61. As is well known, absorption of vaporous ammonia in water is exothermic and the plant cooling Water ilowing through the tubes in exchanger 61 cools the liquid and vaporous contents of the exchanger so as to promote substantially complete absorption of the ammonia in the aqua ammonia. The thus enriched aqua ammonia is passed from exchanger 61 through pipe S6 into separator 54 in which any unabsorbed gases, mostly inerts, are separated from the enriched aqua ammonia. This aqua ammonia contains approximately 491/2 weight percent ammonia and is passed through pipe 22 by pump 5S and heater 60 into the fractionator 11 for recovery of the ammonia as substantially anhydrous ammonia.

A portion of the liquid ammonia from surge tank 38 passes through pipe 41, as a coolant through absorberexchanger 30, and pipe 40 back into tank 38. Another portion is withdrawn from pipe 41 through pipe 42 and is passed into the surge tank 77. Just prior to entering surge tank 77, the pressure of this liquid ammonia is reduced from about 49 p. s. i. a. to about 20 p. s. i. a. by the valve which is `operated in conjunction with the liquid level controller assembly 43. This assembly operates to maintain a constant level of liquid ammonia in this surge tank. Upon reduction in pressure from about 49 p. s. i. a. to 20 p. s. i. a., the temperature of the liquid is reduced from about +20 F. to about 16 F. due to evaporation of ammonia, and the cooled liquid ammonia at this latter temperature provides refrigeration for any desired plant operation. The evaporator 46 which is attached to surge tank 77 by pipes 44 and 47 is a vessel in which heat exchange tubes are placed for providing such refrigeration. Vapors produced in such a heat exchange operation as in vessel 46 are returned through pipe 47 to the surge tank 77. A portion of the liquid ammonia passing through pipe 44 at 20 p. s. i. a. is passed through pipe 45 into surge tank 51. A constant level of liquid ammonia is maintained in surge tank 51 by operation of the liquid level controller assembly 52 and on passing through the valve of this liquid level controller assembly pressure is reduced from 20 p. s. i. a. to about 21/2 p. s. i. a. This pressure reduction drops the temperature of the liquid ammonia from 16 F. to about -80 F. due to ammonia flash @evaporation 'This.;1iqui`d-arn1nonia.atthis ver-ylw ztemperature is availableto provide -extremelyllowdemvpe'rature refrigeration forany desired plant process. evaporator vessel 48 similar to vessel 46 isprovided'with heat exchange tubes, for utilizing refrigeration .at 1

Apparatus A is a rate of flow controller formaintain- 4 ing a constant and uniform ow ofdiash bottoms into the absorber 30. These dilutefiiash bottoms contain about 7 weight percent ammonia andthis relatively-dilute aquaamrnonia absorbs vaporousammonia'from pipe 29 on passage through the absorbing heat exchanger `30. This absorbing heat exchanger Vis maintained :at la relatively low absorption temperature by heat y'exchange with the liquid ammonia from surge tank 38. Aqua ammonia carrying in suspension any undissolved gases `passes through pipe 71 into separator tank 72 in which these fvapors are separated -and are passed through `pipe 73, undervacuum from a vacuum pump 64 in orderA to maintain a pressure of about 3 p. s. i. a. in 'this separator. The aqua ammonia separated in this separator`72 contains Aabout 271/2 weight percentammonia and this liquid is passed through pipe V76, pump 75 and'pipe .26 and is introduced into pipe"78 carrying vaporous arnmoniaenroute from surge tank 77 tolseparator '31. This 271/2 percent ammonia solution has a temperature of about 25 lF. and'in pipe 78 it absorbs substantially allof' the vaporousarnmonia flowing in pipe 78. Upon dissolving this -vaporous ammonia the aqueous ammonia increases -in temperature from about '25 F. to about 70 F. at`20 p. s. i. a. The ammonia concentration ofthe aqueous-ammonia in separator 31 is about 37 weight percent andit is this aqua ammonia solution which is passed through Vpipe and is the absorbent for the waterearnmonia vapors iiowing through pipe 27 from theflash separator 26 into the absorber 61.

Vapors not `absorbed by the aqua ammonia .in absorber 61, as mentioned, are separated in'separator l54 and ,these gases ,are passed through pipe '29A and are combined with the ammonia vapors ilowing through pipe 78 for absorption'in the aqua ammonia from pipe 26.

The vapors not absorbed by this 271/2 percent .aqua ammonia -in pipe 78 are separated in separator '31 and are passed Vthrough pipei'32 and are ultimately addedto the ammonia -vapors flowing through pipe '29.

Vsummarizing these absorption steps, the dilutew-aqua ammonia from the bottom of the flash separator 26-absorbs ammonia vapors in absorber-exchanger 30 at a relatively low pressure to produce `an aqua ammonia of-intermediate concentration. This latter aquaammoniathen absorbs further vaporous ammonia in pipe y78 to produce aqua ammonia of 37 percent concentration which is passed on Vinto the iinalhigh pressure `absorber-exchanger"61 .in which the concentration of ammonia is increased lfrom about 37 percent to about 491A: percentby weight and it is this latter aqua ammonia which is passed to regenerator .11 for recovery of anhydrous ammonia. In this process, Vthe aqua ammonia of lowest concentration is used `to abfsorb vaporous ammonia at the lowest pressure andthe aqua ammonia of highest concentration is used to absorb tthe ammonia vapors at the highest pressure, thus expedit- A ing ammonia recovery.

In the following tabulation is' given in summary form the operating conditions of temperature and pressure and `eoncentrations of ammonia in variousstreams of aqueous ammonia at various points in the process.

1 Stream or Composition "Pressure, Temp., Vessel N 0.1 .p.'-s.i. a. F.

Heating-steam atziap. s. :i.;g (Aqueous) Aq.-NH3 49.5 Wt..per

`-cent NH3 Liq. NH3, 99.5` wt.'.percent` N Hg... 153 95 Aq. NH@ 25 Vwt. percent. N Ham- Aq`NH3A25 wt. per 11t NHs 155 240 rAq. NH3, 'NHS-H2O vapors (51 wt. percent N H3) 50 240 NH3-H20 vapors, 51' wt: percent NH3.. aso Aq. NH3 7 wt. percent N H3..- N H3 vapors 2.' 5 80 AqrNHr, andvapors 3 "25 yAq. N H3, 27.5 wt, percent N H3 Liquid N Hs and vapors 20 1G NH5\vapors Aq. NH3 and vapors-.. 20 75 Aq. NH3 vapors Aq. N H3, 37 wt..percent NH3.- NH3 vapors 49 20 `i8 'NH3 liquidandvepors. -49 20 42 (before expansion) NH3l liquid f 49 20 w18,51 `NH3 liquid and va r.- 22 5 -80 54 Aq.NH3 andvvapor 49 4f95 '57 Plant cooling water 90 The `heaty exchanging absorber which 'I prefer to use `isfthat exemplified specificallyin Figure 2. Such :an ab- :sorber,when operated'asabsorber` 61'of Figure 1, is prefferably.I operated with rits longitudinal axis Idispo'sed `verti- .cally..and `withplant coolingwater Ventering theabsorber -throug'h inlet w57 at the'bottom fand leaving the 'absorber 'through-.outlet581at the top. 'This Water 'on flowing upfward^through this vesselfowsthroughrtheheat exchange x"tubes :86. zin order to .obtain equaldistribution of water through the several tubes 86, section 84'isf-substantially 11a `header se'ctionandzthe outletiendx of this Vexchanger is .falsoprovidedwith a header section 83. These 'header sectionsfalso serve as reducersfsothatthe exchanger can befboltedto `one Lendr thereof'and 1a `pipe for transfer of Athe water bolted 'to'sthe other ends. Theiaquaammonia and rvaporous ammonia for absorption enters :the upper portion .of this exchanger through an inlet. pipe connection 37A and leaves the Vvessel through la'lower outlet ,connection 56A. The aqua ammoniaand'vaporous ammoniall the `major portion ofthis exchanger between the pipes. I have provided contactcpromoting `means within this exchanger to `make-certain of eicient contacting for substantially complete absorption Aof lthe vaporous arntrn'onia by providing trays 87.

These trayscontain openings'90 throughreach of which fis :disposed one .of thewater carryingpipes The diameters for" theseopenings Aare fsome'what greater than `the wouter diameter'opipes 86 `so thatliquid `onthe'trays f-ows downward from tray totray in directcontact with the pipes. The `diameters `of these openingsi areso densigned with respectto the'uter Ediameters of tubes 86 4that there is always .liquid held onV the trays. 'I'hese'trays have upturned "outer yedgesabo'ut A2inches high so :as `to maintain @about 2 inches head `ofzliquid'on -seach o'f `the trays. The `trays falso are made 'of a tslightly smaller @diameter kthan the innerdiarneter `of `thevesselY 61v in Yorder to maintain a free'cross; sectidnalareathrough which unabsorbedgases ma'yf'ow freely with aminirnumpressure drop from tray to tray. Any ainabsorbed rvgases are'ulti- 4mately fentraiiied in the aqua vammonia "andleave-this absorber throughoutlet 56A.

V*Figure -3 is -a `cross-'sectional view on an `enlarged scale `,taken `ionthe line i3-3 of Figure 2 `and'shows the annu- -iarispace 89 between the outer-edge of trays 87 .and the -wall ofthe vessel'and also the Aannularspaces 90 between .the tray and `tubes-86 lfor downow of aqua ammonia.

The bottom of the trays is identified by reference numeral 77 and the Vupturned edge by reference Vnumeral 91. Tubes 86 extend through an'upper header plate 88 and fthrough'afsimilar lower header plate, not shown.

WhileIfhave'described-the use of isuch absorbing heat exchangers as that-illustrated infFigurs 1 and 2 4inA my assente 7 absorption refrigeration process, it is obvious that absorbingheat exchangers of other types can be used such as horlzontallydisposed heat exchangers. I nd, however, that absorbing heat exchangers as illustrated in Figures l and 2 work veryefticiently for absorption of vaporous 1 ammonia lin aqua ammonia as herein disclosed.

The trays are disposed about six inches apart, that is,

- from the bottom of one tray tothe top edge of theY next lower tray is about six inches and the rims 91 atV the edge of the trays are about'two inches high so as to maintain a depth of liquid of about two inches on each tray.

In Figure 1 absorbing heat exchanger 36 is indicated as similar to exchanger 61. While exchanger 61 is described as utilizing water as a coolant, any other suitable coolant can be-used, such as liquid ammonia in the absorbing exchanger 36. In Vexchanger 30 operating with liquid ammonia, the liquid ammonia enters the exchanger at the bottom and leaves at the top, as at 58A, so Vthat vapors formed therein can be easily removed.

Such an absorption refrigeration system as herein disclosed finds use in such-commercial operations as, for example, in the separation of ethylene from mixtureswith ethane and other low boiling gases.

It is obvious that depending upon the particular temperature requirements of any given commercial operation the particular pressures maintained in the Several evaporators, as` evaporators 46 and 48, will be different as is well understood by those skilled in the art. For example if refrigeration at -50 F. were required instead of 80 F. the valve in pipe 45 would lower the pressure of the liquid ammonia from 20 p. s. i. a. to a pressure higher than 2% p. s. i. a., for example about 8 or 9 pounds p. s. i.a.

Under some conditions it may be desirable to employ a third absorbing heat exchanger arranged to promote absorption of ammonia vapors herein described as flowing through pipe 78 in the aqua ammonia from pipe 26. That is, for example, if the refrigeration load required of evaporator 46 were very heavy, very large quantities of ammonia vapors would be produced therein and residence time or considerable cooling would be required to absorb these large volumes of ammonia in this 271/2 percent aqua ammonia. However, without excessive refrigeration requirements in evaporator 46, 1 nd that because ammonia dissolves quite rapidly in aque ammonia a third absorbing heat exchanger is ordinarily not required.

Under some conditions it may be desirable to provide an indirect heat exchanger 60A in order to heat exchange the flash tank vapors passing through pipe 27 with the aqua ammonia feed passing through conduit 22 at a point between heat exchanger 60 and the fractionator 11. When such an indirect heat exchanger is provided the air-iin cooler 59 may or may not be required.

In applying my refrigeration system to an ethylene separation plant in which ethylene is separated and recovered from a mixture containing hydrogen, methane, ethane, ethylene, propane, propylene and other hydrocarbons boiling higher than propane, I have illustrated in Figure l several locations to which member parts of an ethylene plant are attached to utilize the available refrigeration, and furthermore to utilize as efficiently as possible normally available plant cooling water.

At the ammonia condenser 16, plant cooling water from a source, not shown, is introduced into the condenser via a pipe 107, and if desired effluent water can be withdrawn through a pipe 103 for such disposal as desired, or preferably it is passed through a pipe 109 containing a valve 199A, thence through a pipe 124 to an exchanger 123 for cooling aqua ammonia from pipe 26 while absorbing ammonia from pipes 7S and '73A (with valve 121 being closed) in a conduit 122. From exchanger 123 effluent water is passed through pipes 124A, 129 and 57 into the absorber-exchanger 61, and out through pipe 58. Plant cooling water can, under some conditions, be passed through the exchanger 123 (in via pipes-130 and Y changer-absorber 61 (in via pipes 130A and 57 and out 4via pipe 58) and through the condenser 16 in parallel,

each taking plant water at to 90 F., and discharging the waterat somewhat higher temperatures. However, I prefer to pass the plant cooling water through the condenser 16, the exchanger 123 and the absorberexchanger 61 in series. In this latter case, when plant water from a cooling tower enters condenser 16 at about 86 F., it is progressively heated by condenser 16, exchanger 123 and the absorber-exchanger 61 to a temperature of about 103 F. However, the exact temperature of exit of the water will depend upon the rate of water iiow` and the cooling ioad. The temperatures 86 F. and 103 F. are given merely as an illustration of operable temperatures.

In the evaporator 46 is disposed a heat exchanger 143. Pipes 141 and 142, respectively, conduct material to be cooled by liquid ammonia to and from this exchanger.

. In an ethylene plant pipes 141 and 142 provide refrigeration for reuxing a deoiler column which removes C4s and higher boiling hydrocarbons from C3s and lower boiling hydrocarbons and hydrogen, if present.

A heat exchanger 151 is disposed in the evaporator 48 for making available 88 F. refrigeration. Pipes 152 and 153 conduct material to be chilled to and from, respectively, this exchanger. This degree of refrigeration is used in reuxing a demethanizing absorber employed in demethanizing the overhead product of the above mentioned deoiler column containing C3 and C2 hydrocarbons, methane, and hydrogen if present.

In such an ethylene separation system, there is produced an intermediate product containing the C2 hydrocarbons7 i. e. the ethane and the ethylene. rihese latter hydrocarbons are separated from one another in a fractional distillation column, frequently called an ethane-ethylene splitter. An advantageous mode of operating such a column is to supply reboiling heat therefor from the absorber-exchanger 30. Kettle product from the splitter column, not shown, is passed through a pipe 161 containing a valve 162, with valve 163 in pipe 41 being close through the tubes in the `absorber-exchanger 30 and is heated therein. The heated kettle material is withdrawn from the absorber-exchanger through a pipe 164, with the valve in pipe 46 being closed. This withdrawn heated material is then passed to the reboiler of the splitter column for imparting reboiling heat thereto.

Regenerator column 11 can, under some conditions, be operated at a higher kettle temperature and pressure than hereinbefore disclosed to furnish heat for reboiling the aforementioned demethanizer-absorber. Heat is furnished for reboiling the aforementioned demethanizer-absorher by passing the hot weak aqua ammonia from the kettle of the column 11 through pipes 13, 23, exchanger 24, and pipes 63 and 191 with the appropriate valves including valve 1415 being open and valves 101. and 101A being closed. Valve 166 also is closed. A stream of demethanizer-absorber kettle product is passed through a pipe 134, exchanger Z4 and through a pipe 105 for return to the demethanizer-absorber kettle to deliver its heat. In this manner exchanger 24 serves to heat the demethanizerabsorber kettle material and as a cooler for the weak aqua ammonia from the fractionator 11.

Additional reboiling ieat for the demethanizer-absorber column is sometimes required and such additional heat is provided by a heat exchanger 126 in a line 125 through which aqua ammonia is passing from pipe 35 and separator 31. When this additional reboiling heat is required a portion of the kettle contents of the demethanizer-absorber column is passed via a pipe 128 to exchanger 126 and thence returned to the reboiler via a pipe 127. While Vkettle product from the reboiler of the demethanizerabsorber can be passed through the exchanger 24 and the exchanger 126 in series, it is preferable to pass separate streams of the kettle material through these exchangers,

"9 i. .el-imparallel. When vexchanger 1,216 iswsefvice; the valve in pipe V31S is closed and the valves in Ac onduitq-lZS lare open, and when this exchanger is not inservice,;--the -valves in pipe 125 are closed and the valve. in pipe 35 is open.

When the distillation column 11 is operated yat a higher pressure and higher kettle temperature than hereinbefore disclosed, the exchanger 24 is operated'asza cooler, as mentioned, and the iiash ,tank 26 is bypassed, `the yconcentration of vammonia in the aqua ammonia in pipe 28 is not much different than when `the still `is operated with .exhaust steam and the exchanger 24-is :a heater `and the ash tank is used. The operation of subsequent steps is `not altered appreciably.

While `certain embodiments of the invention have been described for illustrative purposes, the invention obviously is. not limited thereto.

I claim:

l. A method for providing refrigeration which comprises flashing liquid ammonia insuccessively lower pressure dashing steps to cool the unvaporized ammonia to Vd esired refrigeration temperatures, absorbing the flashed ammonia, in aqueous ammonia of progressively `increased concentrations of ammonia inprogressivelyhigherV temperature and pressure absorption steps, passing the finally `produced aqueous `ammonia into airaetionation column and thereinfractionating said aqueous ammonia .under superatrnospheric pressure to produce an overhead va- =porous ammonia product and a bottoms product ofaqueous ammonia more dilute than -the aqueous ammonia passed into the column as-feed, condensing said .overhead vaporous ammonia to produce liquid ammonia, reducing `the pressure on the aqueous ammonia bottoms product in a bottoms dashing operation, removing flash vapors of aqueous ammoniav lfrom this bottoms ashing operation and passing same into lthe absorption step` of highest pressure and temperature of the successive absorption. steps, .cooling the ash bottoms of said bottoms flashing operation in indirect heat `exchange .withthe aqueous .ammonia feed to said column, passing the" cooled ilash bottoms of said bottoms flashing operation into the absorption step .of lowest pressure and temperatureof the successive absorption steps, cooling the aqueous ,ammonia and vaporous yammonia ofthe `highest pressure absorption step by indirect heat exchange with plant cooling water and cooling the xaqueous ammonia and vaporous ammonia of the lowest pressure absorption step by indirect heat exchange =.with `.the condensed "liquid ammonia.

2. A method for providing refrigeration which comprises ashing lquid ammonia in successively lower pressure dashing steps to cool the unvaporized ammonia to desired refrigeration temperatures, absorbing the ashed ammonia in aqueous ammonia of progressively increased concentrations of ammonia in progressively higher pressure absorption steps, passing the nally produced aqueous ammonia into a fractionation column and therein fractionating said aqueous ammonia under superatmospheric pressure to produce an overhead vaporous ammonia product and a bottoms product of aqueous ammonia more dilute than the aqueous ammonia passed into the colunm feed, condensing said overhead vaporous ammonia to produce liquid ammonia, reducing the pressure on the aqueous ammonia bottoms product in a bottoms dashing operation, removing ash vapors of aqueous ammonia from this bottoms flashing operation and passing same into the absorption step of highest pressure of the successive absorption steps, passing the ash bottoms of said bottoms ilashing operation into the absorption step of lowest pressure of the successive absorption steps, cooling the aqueous ammonia and vaporous ammonia of the highest pressure absorption step by indirect heat exchange with plant cooling water and cooling the aqueous ammonia and vaporous ammonia of the lowest pressure absorption step 10 :fby` indirect vheat:.aichange =the=.condensed "liquid-arrismonia.

r3.' Inthemethod .of `claim -2 carrying .outithe fraction- .ating Loper-ation by heating 'the kettle ofvthe fractionator .5 indirectly with normally waste plant steam.

l4. A methodfor `providing refrigeration. comprising :cooling liquidaminonia by reducing `the pressure thereon .'rom agsuperatmospheric pressure .in a rst tlash vaporizing step, thereby producing-inst.ammoniailash vapors and-a iirst cooled liquid ammonia, absorbingtherst am- `inonia flash yvapors and .ammoniafwater vaporous stream 4as subseqi'lentlyproduced in an aqueous .ammonia ,of intermediate ammonia concentration as subsequently y,produced in an indirect heat exchange operation with plant cooling `water-,to .produce a concentrated vaqueous ammonia, distilling said concentrated aqueous ammonia y:to produce an overhead vaporous ammonia product and a -dilute liquid aqueous ammonia bottoms product, condensingA said overhead vaporousamrnoniato-produce the first mentioned Vliquid ammonia, reducing thepressure of said .aqueous Vammonia bottoms product in a second dashing `operationthereby producing said ammonia-water vaporous strearn as subsequentlyproduced.and a second liquid aque- ,ousammoniawash bottoms oflower ammonia concentra- `trationfthan said Adiluteaqueous ammonia bottoms prod- .uct, reducing the pressure :on said' iirst cooled liquid arnmonia in a third ash vaporizing step thereby producing ,second ammonia-,flash vapors and second cooled liquid Aammonia at 4a` rst desired 'refrigeration temperature, ab- .,sorbing said secondamrnonia flash vapors in an aqueous ammoniaof concentration lower than said intermediate ammonia concentration as 4subsequently produced at the .pressure of lsaid-third -tash vaporizing step to produce Hsaid aqueous ammonia of :intermediate ammonia conceny tration y-as `subsequentlyproduced, reducing the pressure on the cooled liquidvarnmoniaat said rst desired refrigeraqtionlin a Yfour-.thA Hash Ivaporizing step thereby producing third ammonia yiiash vapors and athird cooled liquid am- Inoniaat a second `desired refrigeration temperature lower .than said tirst desired refrigeration temperature, absorbing said Athird ammonia -ilash vapors in said second liquid aqueous ammoniailash `bottoms in an indirect heat ex- `change operation with s aid first cooled liquid ammonia to-produce said aqueous ammonia Aof concentration lower Man saidintermediate ammonia concentration as subsenuentl-y produced.

.5 In the method `of Aclaim 4` wherein the heat for reg.the fractionation operation is about 15 pound Mes i'e s teaniythe fractionator pressure is about 155 p. s. i. a. and the kettle temperature is about 240 F.

6. In the method of claim 4 wherein the pressure of the second flashing operation is about p. s. i. a.

7. In the method of claim 4 wherein the pressure of the rst, third and fourth ashing steps are about 49 p. s. i. a., 20 p. s. i. a. and 2.5 p. s. i. a., respectively.

8. In the method of claim l, condensing said overhead vaporous ammonia to produce liquid ammonia by indirect heat exchange with plant water, passing the plant water from the overhead ammonia condensing step serially in indirect heat exchange with vaporous ammonia undergoing absorption in aqua ammonia in two progressively higher temperature and higher pressure absorption steps.

9. In the method of claim l, cooling said bottoms product of aqua ammonia by indirect heat exchange with the kettle product of a demethanizer-absorber producing an overhead product comprising methane anda kettle product comprising ethane, ethylene, propane and propylene from a feed stock comprising said methane, ethane, ethylene, propane and propylene, thereby providing reboiling heat to the kettle of said demethanizer-absorber.

l0. In the method of claim l indirect heat exchanging the flashing liquid ammonia of the lowest pressure liquid ammonia flashing step of the successively lower pressure liquid ammonia dashing steps, with the contents of the upper portion of a demethanizer-absorber operating to produce an overhead product'comprsing methane and a kettle product comprising ethane, ethylene, propane, propylene from a feed stock comprising said hydrocarbons, thereby providing reflux for said demethanizer-absorber.

11. In the method of claim 1, cooling the flashed ammonia vapors undergoing absorption in the aqueous ammonia of the lowest ammonia concentration of the aqueous ammonia solutions of progressively increased concentrations of ammonia in indirect heat exchange with the kettle product of an ethane-ethylene fractionating column operating to produce an overhead product comprising ethylene and a kettle product comprising ethane from a feed stock comprising these two hydrocarbons, thereby providing reboiling heat to the kettle of said ethaneethylene fractionating column.

12. In the method of claim 1 cooling the aqua am- -monia Ysolution of the next lowest concentration of ammonia of the aqua ammonia solutions of progressively increased concentrations of ammonia by indirect heat exchange with the kettle product of a demethanizer-absorbet' producing an overhead product comprising methane and a kettle product comprising ethane, ethylene, propane and propylene from a feed stock comprising said methane, ethane, ethylene, propane and propylene, thereby providing reboiling heat to the kettle of said demethanizer-absorber.

13. A method for providing refrigeration comprising cooling liquid ammonia by reducing the pressure thereon from a superatmospheric pressure in a first flash vaporizing step, thereby producing first ammonia flash vapors and a first cooled liquid ammonia, absorbing the first ammonia llash vapors and an ammonia-water vaporous stream as subsequently produced in an aqueous ammonia of intermediate ammonia concentration as subsequently produced in an indirect heat exchange operation with plant cooling water to produce a concentrated aqueous ammonia, the absorbing operation comprising introducing said rst ammonia ash vapors, said ammonia-water vaporous stream and said aqueous ammonia of intermediate concentration into the upper portion of an absorbing heat exchange zone, passing these introduced materials downward in said zone in indirect heat exchange with upflowing cooling medium thereby producing a cool concentrated aqueous ammonia, withdrawing this cool concentrated aqueous ammonia from the lower portion of said zone, distillin7 the withdrawn concentrated aqueous ammonia to produce an overhead vaporous ammonia product and a dilute liquid aqueous ammonia bottoms product, condensing said overhead vaporous ammonia to produce the rst mentioned liquid ammonia, reducing the pressure of saidaqueous ammonia bottoms product in a second ashing operation thereby producing said arnmonia-Water vaporous stream as subsequently produced and a second liquid aqueous ammonia Hash bottoms of lower ammonia concentration than said dilute aqueous ammonia bottoms product, reducing the pressure on said tirst cooled liquid ammonia in a third Yllash vaporizing step thereby producing second ammonia flash vapors and second cooled liquid ammonia at a first desired refrigeration temperature, absorbing said second ammonia ash vapors in an aqueous ammonia of concentration lower than said intermediate ammonia concentration as subsequently produced at the pressure of said third flash vaporizing step to produce said aqueous ammonia of intermediate ammonia concentration as subsequently produced, reducing the pressure on the cooled liquid ammonia at said irst desired refrigeration in a fourth ash vaporizing step thereby producing third ammonia Hash vapors and a third cooled liquid ammonia at a second desired refrigeration temperature lower than said first desired refrigeration temperature, absorbing said third ammonia ash vapors in said second liquid aqueous ammonia flash bottoms in an indirect heat exchange operation with said rst cooled liquid ammonia to produce said aqueous ammonia of concentration lower than said intermediate ammonia concentration as subsequently produced.

14. In the method of claim 4 wherein said rst and second desired refrigeration temperatures are about "16 F. and F., respectively.

References Cited in the file of this patent UNITED STATES PATENTS 1,425,019 Jordan Aug. 8, 1922 2,103,596 Raigorodsky Dec. 28, 1937 2,216,175 Helbing Oct. l, 1940 2,248,178 Kuenzli Iuly 8, 1941 2,253,892 Clayton Aug. 26, 1941 2,336,097 Hutchinson Dec. 7, 1943 2,392,894 Zwickl Ian. 15, 1946 2,519,618 Wilson Aug. 22, 1950 2,548,508 Wolfner Apr. 10, 1951 2,610,038 Phillips Sept. 9, 1952 FOREIGN PATENTS 553,485 Great Britain May 24, 1943 

1. A METHOD FOR PROVIDING REFRIGERATION WHICH COMPRISES FLASHING LIQUID AMMONIA IN SUCCESSIVELY LOWER PRESSURE FLASHING STEPS TO COOL THE UNVAPORIZED AMMONIA TO DESIRED REFRIGERATION TEMPERATURES, ABSORBING THE FLASHED AMMONIA IN AQUEOUS AMMONIA OF PROGRESSIVELY INCREASED CONCENTRATIONS OF AMMONIA IN PROGRESSIVELY HIGHER TEMPERATURE AND PRESSURE ABSORPTION STEPS, PASSING THE FINALLY PRODUCED AQUEOUS AMMONIA INTO A FRACTIONATION COLUMN AND THEREIN FRACTIONATING SAID AQUEOUS AMMONIA UNDER SUPERATMOSPHERIC PRESSURE TO PRODUCE AN OVERHEAD VAPOROUS AMMONIA PRODUCT AND A BOTTOMS PRODUCT OF AQUEOUS AMMONIA MORE DILUTE THAN THE AQUEOUS AMMONIA PASSED INTO THE COLUMN AS FEED, CONDENSING SAID OVERHEAD VAPOROUS AMMONIA TO PRODUCE LIQUID AMMONIA, REDUCING THE PRESSURE ON THE AQUEOUS AMMONIA BOTTOMS PRODUCT IN A BOTTOMS FLASHING OPERATION, REMOVING FLASH VAPORS OF AQUEOUS AMMONIA FROM THIS BOTTOMS FLASHING OPERATION AND PASSING SAME INTO THE ABSORPTION STEP OF HIGHEST PRESSURE AND TEMPERATURE OF THE SUCCESSIVE ABSORPTION STEPS, COOLING THE FLASH BOTTOMS OF SAID BOTTOMS FLASHING OPERATION IN INDIRECT HEAT EXCHANGE WITH THE AQUEOUS AMMONIA FEED TO SAID COLUMN, PASSING THE COOLED FLASH BOTTOMS OF SAID BOTTOMS FLASHING OPERATION INTO THE ABSORPTION STEP OF LOWEST PRESSURE AND TEMPERATURE OF THE SUCCESSIVE ABSORPTION STEPS, COOLING THE AQUEOUS AMMONIA AND VAPOROUS AMMONIA OF THE HIGHEST PRESSURE ABSORPTION STEP BY INDIRECT HEAT EXCHANGE WITH PLANT COOLING WATER AND COOLING THE AQUEOUS AMMONIA AND VAPOROUS AMMONIA OF THE LOWEST PRESSURE ABSORPTION STEP BY INDIRECT HEAT EXCHANGE WITH THE CONDENSED LIQUID AMMONIA. 